1. Field of the Invention
The invention relates to a power supply for use for operating an ultrasonic transducer for carrying out welding or bonding operations on circuits such as integrated circuits.
2. Description of the Prior Art
Ultrasonic transducers for welding purposes have been employed for many years as exemplified by U.S. Pat. Nos. 3,054,309; 5,201,454; and 5,244,140 which are incorporated herein by reference. The transducers generally are formed of stainless steel and have a welding end for supporting a welding tool for holding a wire to be welded to an integrated circuit (IC) or to a carrier package. The opposite end supports a source such as a piezoelectric ceramic crystal device for causing the body to vibrate at a desired frequency for welding purposes. A mount is provided for supporting the transducer and the piezoelectric crystal device is driven by a power supply for operating the transducer for a given bonding cycle.
Problems have occurred in that parameters such as temperature and the force exerted on the bond pad including clamping forces change which causes the impedance of the transducer to change. If the impedance increases, the power to the transducer decreases which decreases the quality of the weld resulting in an unreliable IC. The impedance changes also can also be caused by long term drift changes in the piezo material characteristics, chemical composition of the bonding surface, bonding wire type, bonding wire material transducer mounting torque variations, bonding tool size and type, bonding tool installation variations, bonding site tool contact pressure during bonding, variations in the formation of inter metallic chemistry at the bond site during bonding, and variations in the bonding ball size.
It also has been found that the conventional bonding cycle is not fast enough and that the IC can be subjected to heat for an extended period which can result in damage to the IC.